Ink-jet printers are used for, e.g., displays, posters and bulletin boards. Non-porous recording media such as plastics are mainly used for industry use, and inks for such a use are being developed. Solvent ink-jet inks including a resin dissolved in a vehicle such as an organic solvent, and ultra-violet curable resin ink-jet inks including a polymerizable monomer as a main component, are used as ink-jet recording inks for industry use. However, water based inks, which have been widely used for home use and which are favorable in terms of their low environmental impact, are being developed for industry use.
Examples of non-porous recording media for industry use include non-transparent substrates such as PVC (polyvinyl chloride), and tarpaulin, and transparent substrates such as PET (polyethylene telephthalate), PP (polypropylene), and PE (polyethylene). However, a recording medium printed with a monolayer does not come out well due to shadowing on the other side when printing on transparent substrates. Multiple layer printing, which is printing over a prior printed substrate, is also used. However, multiple layer printing has a problem in that image cissing occurs when printing an upper layer over a lower ink layer. To resolve this problem, a different amount of surfactant is added in each of the upper layer and the lower layer (see Patent literature 1: Japanese Patent Application Laid-Open Publication No 2013-828852).